Special Edition ~ Perseid Meteor Shower Imminent

Big Meteor Shower Expected Thursday~Friday-Saturday

SKYWATCH

The Famous Perseid Meteor Showers ~ Now Through Aug 23

  I added an abbreviated Perseid Skywatch section to my July issue two days after it was published, so if you were an “early viewer”, you probably didn’t see it. Below is the expanded version – with an update from Friday down below.

   “Shooting stars” or “falling stars” (in español lluvia de estrellas “rain of stars”) the Perseids are arguably the favorite of the Northern Hemisphere meteor-watching set, both because they can put on quite a show and because it’s “summertime and the viewin’ is easy”. The show this year promises to be more spectacular than usual because the pros say they’ll be in “outburst” mode ~ the last time being 2009.  They are thus expected to appear at twice their typical rate at their peak Thursday night/Friday morning.

Meteor Shower (composite)

   Space.com quotes NASA meteor expert Bill Cooke: “This year, instead of seeing about 80 Perseids per hour, the rate could top 150 and even approach 200 meteors per hour.” According to my calculator, that’s 2 1/2 to 3 per minute, or approximately one every 18 to 24 seconds.

   Will it look like the above picture? No ~ that photo is a composite of frames taken over an hour or so. Each individual streak in the sky will look more like this:

Perseid meteor 2015 (eltiempo.es)

Perseid meteor 2015 (eltiempo.es)

  There’s no sound accompanying them, so it’s an entirely different experience than watching/hearing earthbound fireworks. If you’re moved by the silent spectacularness of nature, then this would be for you.

Where and how
.   A dark sky ~ any place away from city lights where you can see most of the open sky ~ the darker the better. (Of course, a clear sky without clouds is the best, but even with scattered clouds you can still see a lot.) A lawn chair that you can tilt way back or lie flat on, or a blanket on the ground are your best setup. You won’t need binoculars; they would in fact get in the way.

   Here is a diagram showing where to aim your head. Although meteors can streak just about anywhere, the radiant or apparent source of all Perseids is from the top of the constellation Perseus.

Perseid radiant location

Perseid radiant location (Sky & Telescope)

   I like this diagram because it locates Perseus in relation to Cassiopeia. Cassiopeia is one of the most conspicuous constellations right now because of her bright stars that sit in the shape of a recognizable “W”.

When
.   Although Earth entered the outer edge of Comet Swift-Tuttle’s orbital path (and thus its debris trail that is the source of the Perseid meteors) on July 17, their frequency is increasing now, with computer models predicting the main show in the wee hours before dawn on Thursday, Friday, and Saturday (11, 12, and 13), with the expected outburst beginning Thursday evening and running into Friday morning.  
If you’re a graphy kind of person, here is a chart of predicted Perseid performance:

Perseids predicted ZHR (2016) [NASA]

Predicted Perseids ZHR (2016) [Bill Cooke NASA]

   Note that the ZHR (zenithal hourly rate ) (quoting now from the U.K.’s Telegraph website) “…is a normalised quantity based on how many meteors you’d see under perfect conditions watching the whole sky with the radiant directly above your head. The true visual rate will be lower and you can expect to see anywhere between 20-50 meteors per hour around Perseid maximum.” Note that while the rate drops precipitously after Aug 12, the show will continue in a less dramatic way all the way to Aug 23. So if you’re out before dawn on any of these warm summer nights, there’s natural entertainment awaiting you.

    So there you have it. Because of the space mechanics involved (the leading side of Earth “scoops up” these tiny grains of sand as it passes through the comet’s debris trail), your best bet is in the window from around midnight until dawn wherever you are, although people have been reporting sightings as early as 10 pm. And this year, though the moon will not exactly be cooperating to her fullest (as she will be waxing gibbous), she will be setting around midnight to 2 a.m. this week, so not a show-stopper. (You can check mooonrise and moonset times where you are by going to Time and Date and plugging in your location.)

  If you’re still with us and interested in more details, good sites are space.com,  EarthSky, Sky&Telescope, and this Washington Post article. Or just search for “Perseids”.

   Happy viewing!

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   [Update Friday 12 Aug]
.   I stayed out until 3am this morning and was rather disappointed. I went out to a hill near me where I had a view of the entire dome of the sky. In an hour’s span I saw just three bright streaks and two dim ones. Nice, but not the flurry I was expecting. Here are some mediating factors that affected my viewing and may be of interest to you.

   Transparency and darkness:  Most of the meteors are of the faint type, as they are produced by the smaller grains of sand that constitute the bulk of the comet’s debris trail. To see these, you must have access to a completely clear and dark sky, not compromised by city lights or moonlight. Additionally, you need to give yourself about 20 minutes to accustom your eyes to the dark.
.  In my case this morning there were a few spotty thin clouds and, while I wasn’t surrounded by city lights, there was a city area below me only about a mile away. So even though the sky dome above me looked black, it wasn’t the deep black of the clear, dark sky I recall from the desert the last time I went Perseid hunting.
.  So how can you tell how dark and clear your sky is? The best way is to judge by the density of stars you can see. Here is a good visual comparison, courtesy of the L.A. Times:

Dark sky comparisons (LA Times)

Dark sky comparisons (L.A. Times)

    What I had was the “Suburban sky”. That means I could make out prominent star formations, such as Cassiopeia, but it wasn’t dark enough to allow fainter stars to be visible. Thus I probably was missing a bunch of fainter meteors. I was treated to three fiery streaks, so that was cool! I may look again tomorrow if I get myself up early enough before dawn.

   I hope you got to see some! We’ll track meteor showers in the future and let you know about any promising ones.

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    Thanks for taking a look at this special edition of EM&S.

   Full moon Wednesday/Thursday next week.  Check back for our August full moon issue, coming out early next week. Or sign up to follow us and receive an email notice from WordPress for each “moonthly” issue.

   ~Marty (a.k.a. Aquarianman)

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About aquarianman

Aquarian interested in anything to do with the Earth, our Moon, and anything flying around out there in space.
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